Inside the M45 headroom equals 1,011 mm (39.8 in) front and 947 mm (37.3 in) rear, with 1,389 mm (54.7 in) front and 1,374 mm (54.1) in rear shoulder room, 1,387 mm (54.6 in) front 1,339 mm (52.7 in) rear hip room and the all important 1,069 mm (42.1 in) front and 826 mm (32.5 in) rear legroom. This compares well with the Q45 for interior spaciousness with the M getting 36 mm (1.4 in) more headroom in the front and 23 mm (0.9 in) in the rear, granted the Q's specs include a sunroof. The remaining interior dimensions favor the Q45, with 89 mm (3.5 in) less front and 79 mm (3.1 in) less rear shoulder room, 48 mm (1.9 in) less front and 58 mm (2.3 in) less rear hip room and a reduction of (1.9 in) up front and a whopping (4.8 in) in the rear for legroom. The M's trunk volume is only slightly marginalized at 379 L (13.4 cu ft) compared with the Q's 385 L (13.6 cu ft) volume.
But comparing capacities and dimensions brings up a strange contrast. According to Nissan's preliminary specifications the M weighs in at 1747 kg (3,851 lbs), a full 22 kg (50 lbs) heavier than the 1724 kg (3,801 lbs) Q. What gives? Does the new M45 need to go on a radical protein diet before it hits the market? Not really. This oddity has more to do with the Q45's extremely spry weight rather than any obesity on the part of the new Infiniti. The benchmark BMW 540 weighs in at 1,700 kg (3,748 lb), the same weight as the Lexus GS 430, which is only 47 kg (103 lb) lighter than the midsize Infiniti. That said the Audi A6 4.2 weighs 1,825 kg (4,023 lb), 78 kilos (172 lbs) more than the M45.
The truth to its power to weight ratio will unfold on the open road, where the Infiniti's superb 340 hp, 4.5-L 32-valve, DOHC V8 with 333 lb-ft torque should allow for quick getaways. In comparison the heavier Audi A6 4.2 can only muster 300-hp and 295 lb-ft of torque while the BMW 540 puts out 290-hp and 324 lb-ft of torque. The Lexus GS 430 of the same weight produces 300-hp and 325 lb-ft of torque. The 2003 Mercedes-Benz E500 will deliver 302-hp and 339 lb-ft of torque and so as not to leave it out, the 2003 Jaguar S-Type 4.2 weighs in at 1,735 kg (3,825 lb) and delivers 300-hp and 310 lb-ft of torque putting it about mid-pack. All said the Infiniti M45 should produce quicker acceleration off the line than any of its competitors for the time being. Its 5-speed automatic transmission with manual shift mode driving the rear wheels is par for the course in this lofty territory.