As said above, the wider the tire, the more traction you get.
Sway bars are, in my opinion, the last thing to "upgrade". Start with something known to be good, such as good rear end bushings, good front end bushings, wider than stock tires, etc to get more traction. Replace all the 20 year old, worn out stuff so that you're starting with everything fresh, then see what needs tweaked.
The 225 series tires will give you better MPG, but be a limiting factor when cornering due to small contact patch. My question is, assuming you have 225 front, 275 rear, is that for better straight line acceleration, or for appearance?
I like having same size all around when possible, since tires aren't cheap, I like to rotate them (front to back for me as mine are directional) to get more life out of them, and you can't do that staggered. I run 255's all around, and with good suspension, she corners very well.
So, long story short, what are your goals?
97 Thunderbird LX (The GT Bird)
2003 Explorer WAP block with Modular Head Shop "street ported" heads and Stage 2 PI NA cams, 75mm Accufab throttle body, C&L upper intake plenum, Kooks 1.75" primary/3" collector headers, 2.5" full exhaust with mid mount Magnaflow dual in/out muffler, 24lb/hr injectors, 80mm MAF, Tuning from Don @ www.lasotaracing.com
, CAI that feeds from fenderwell. Jmod, 3.73:1 TL in Mark VIII carrier, Mark VIII aluminum LCAs, 93 Mark VIII driveshaft, PBR brakes (soon to be Cobras), 18x9 wheels with 35mm offset, 255/40/ZR18 Tires, Front and Rear strut/shock bracing, GR-2 shocks, Eibach 1.5" springs, 1989 SC front and rear sway bars.