Both are very excellent addons. Like the P-51 vs B-17 thread, it is mostly about what type of flying you like to do. Both are very unique experiences. The 377 is a large multi engine aircraft, with systems and flying proceedures to match.
The P-40 is a rugged single seat fighter with the style and systems to match. Of all the A2A fighters so far I still believe the P-40 is the best suited to low level scenery exploration involving multiple takeoffs and landings. It really does have an 'attitude' that is a perfect match for the likes of Wild Bill Kelso from the movie '1941'...it will run on 91 Octane...guess thats why Wild Bill liked to fill up at gas stations
With your system specs the P-40 might be preferable too because being a single engine fighter and a little bit simpler systems wise.
"The knack of flying is learning how to throw yourself at the ground and miss." - Douglas Adams