T-8's with the correct electronic ballast will equal or better the old T-12s at the reduced wattage - a rule to follow is the narrower the tube, the higher efficiency; unless you had high-output ballasts and were cooking the T-12s. Example: There are high-output 8-foot 86 watt T-8 bulbs that will pump out 7,600 lumens; to match that output in a 96" T-12 would take 110 watt bulbs. BUT the ballast has to be tuned to the circuit, relamping with T-8 bulbs using a T-12 vintage ballast can produce erratic results.
Take care selecting ballast and bulbs from manufacturers products matrix, all the lumen outputs - wattage inputs are provided. To get the most from your current fixtures may mean swapping the holder-socket types to single pin or the high-output nub style. If you want real light look into T-5 bulbs, very pricey. I've re-ballasted 96" fixtures with electronic ballasts but the homeowner declined buying the T-8 bulbs so the T-12s were reused and they never appeared to really light if you know what I mean - even and instant light but just not dazzling bright.
If you have voltage transients, brown-outs on equipment or A/C start up or lightning or other spikes, or dead air-space allowing over-temperature, you need to find out what is reducing the life of your current ballasts! Also, know the CFL ballasts are extremely more likely to be affected by supply or location problems than the mature canned ballast types. My opinion on CFL's is they are hit or miss on quality, and definitely do not tolerate short run times like flicking on lights for a few minutes only.