Normal words of wisdom from snowy Canada are your non-winter tires start to lose effectiveness around 8'C. Since you only ever get down to maybe 5'C...I'd say you could go with performance summers over all seasons no problem. I don't think they'd be any safer...Primacy's are good tires...but you can get softer rubber compounds in summer tires which will provide increased grip...at the expense of wearing out sooner (I go by the rating 280 is very soft, 400 is what I ran on my Altimas...and 600+ are eco-friendly, high mileage tires..but often noisy and less capable.
You cannot 'tune' the car to handle different wheel diameters...you need to try to keep the wheel size about the same (within 1% or so). In general for every 10mm in width, you need to drop 5% in profile...ie 215/55 are about the same size as 225/50's. There's no way a 295/40 is anywhere close to the same size as a 215/55. You could probably squeak the 235/50's on to your rims, clear the suspension parts, and only have minor errors in the speedometer.
I don't know what the roads you drive on are like, but going to profiles in the 30-40 range dramatically increases your risk of rim damage due to curbs, cracks holes, debris etc. but will provide a more responsive steering feel...in as much as that's possible with an Altima
You pay a lot more for these tires too.
You cannot 'tune' the car to handle different wheel diameters...you need to try to keep the wheel size about the same (within 1% or so). In general for every 10mm in width, you need to drop 5% in profile...ie 215/55 are about the same size as 225/50's. There's no way a 295/40 is anywhere close to the same size as a 215/55. You could probably squeak the 235/50's on to your rims, clear the suspension parts, and only have minor errors in the speedometer.
I don't know what the roads you drive on are like, but going to profiles in the 30-40 range dramatically increases your risk of rim damage due to curbs, cracks holes, debris etc. but will provide a more responsive steering feel...in as much as that's possible with an Altima