I like Jack Daniels VDOT calculator, the only problem comes when your last race was 100 miles. VDOT is based on recent race results so my workout today was more by feel than anything. 10 X 200 on a rolling 3/4 mile stretch of dirt road between 8100-8300 altitude. No straining or pushing, the thought was more to relax and hold good form with out ever feeling like I couldn't speed up. The fastest was 33" and the slowest was 37". Some were down, some were up and I used my GPS so the precise measurements are questionable (I used .13mi just to be sure), but the legs were definitely there despite a big week of training both running and biking and it felt great to run fast.
Over the past few years my biggest weakness has been my extensive focus on base. My base fitness would be huge with MAF tests that averaged in the 5:50 pace range, but what I lacked was lactate development and comfort for extended periods of times at a fast pace. A lack of muscular development to handle fast paces really. So hopefully I can change my ways and address the issue this year.
Every time I think about possible races this year, the Denver Marathon pops in to my head. I think it might be perfect for me as I would drop ~3000ft in altitude, it isn't flat, and it's ~40:00 from my house.