Pontiac’s flagship Bonneville GXP is something of a “sleeper” among reasonably priced performance/luxury sedans. It’s never been as flashy as the Grand Prix or GTO, but it’s a highly competent car that deserves a close look from anyone in the market for an athletic, full-size sedan.

The Bonneville received a total makeover in 2004, so the 2005 models are essentially unchanged except for some minor appearance upgrades on the mid-model SLE. The previous top model SSEi with its supercharged V-6 was a surprisingly strong performer, but it’s been capably replaced by the new GXP. We drove the Bonneville GXP and liked it better than the SSEi, because the styling, refinement, and performance have all been substantially improved.

A key to the Bonneville GXP’s impressive performance is the 275 horsepower version of Cadillac’s great 4.6-liter Northstar V-8. The Northstar engine is exclusive to the GXP. The base SE and mid-level SLE use the normally aspirated 205 horsepower 3.8-liter V-6. All Bonnevilles are front-wheel-drive.

The Northstar V-8 joins a long list of impressive engines that have powered Bonnevilles ever since their debut in 1957. The original limited production Bonneville (one per dealership: total 630) convertible was equipped with Pontiac’s first fuel injected engine, a 347 cubic inch V-8. Those chrome and steel icons can easily command six figures today.

Bonneville V-8’s grew to 455 cubic inches before falling to 301 in the late eighties. Then came the V-6’s which gradually evolved into potent powerplants capped by the supercharged 240 horsepower 3.8-liter V-6 in the 2003 Bonneville SSEi.

Anyone familiar with Northstar-powered Cadillacs or Olds Auroras will love the new Bonneville GXP. It’s one of the smoothest engines ever made by General Motors and an excellent match for the big Bonneville. Even though Pontiac gets 15 less horsepower than Cadillac there isn’t a sense that anything is missing. Pontiac claims sub-seven second 0-60 mph times, which feels about right.

Previous Bonnevilles were a little heavy on body cladding, ribs, and scoops. The new Bonneville GXP’s styling is much more purposeful. Standard 18-inch five-spoke alloy wheels are as slick as any aftermarket wheels. Big brakes with bright red calipers show through the spokes.

Speaking of a bright red, our GXP test car was Crimson Tintcoat, a $750 option. That seemed steep for metallic paint until the sun came out. The color’s brilliant beauty easily justifies the price. The best option on the Bonneville is the Eyecue Heads Up Display. It should be a mandatory safety option. You can monitor speed in your peripheral vision without taking your eyes off traffic

The Bonneville GXP not only looks and performs well, it also sounds great. Four chrome exhaust tips emit just enough V-8 rumble to fondly recall past Pontiacs, but don’t make so much noise that you regret choosing the GXP. The lower than normal 3.7:1 final drive ratio and adaptive shift logic four-speed automatic transmission help the Bonneville move out smartly. There’s a hint of torque steer under hard acceleration, but nothing disconcerting. The Bonneville GXP is an adult hot rod.

Considering the Bonneville’s full-size heft it handles quite well. Structural rigidity was significantly increased and a strut tower brace was added. DeCarbon gas shock absorbers, Goodyear Eagle 235/50R18 tires, traction control, and large vented brakes all contribute to the surprisingly athletic handling of the almost two ton sedan.

Great interior comfort has always been a Bonneville trademark and the GXP is no exception. Front legroom is of the stretch-out variety and rear seat room is ample even with the front seats all the way back. Trunk space is cavernous.

Pontiacs have some of our favorite steering wheels. They place essential audio controls where you can use them without being distracted. Those controls are helpful when there are so many entertainment options. Our GXP had the 8-speaker Monsoon sound system with CD player, AM/FM, and cassette plus the optional XM satellite radio with its 100 stations.

Whines: The interior HVAC vents were overly busy and the faux carbon fiber trim looked like cheap plastic to us. The XM radio cut out too often (not Pontiac’s fault) during punch lines on the comedy channels.

Bottom Line: The Pontiac Bonneville GXP is a great combination of handsome styling, strong performance, spacious accommodations, luxurious appointments, good fuel economy, and a huge trunk with base prices ranging from $28,000 to $36,000 depending on model. We were just as impressed with the new Pontiac Bonneville GXP as we were with the first Northstar V-8 powered Cadillac Seville STS. It’s great to have all the benefits of a full size sedan without giving up performance. We think the Bonneville GXP is the best Bonneville ever.