You have a point, Stew but.....I've done simple halflife plots of omna/sust and enanthate and they really aren't that different. If (this is a big if) the model for entering the bloodstream and leaving the oil injected IM is exponential decay, you are pretty front loaded with anything. For steady blood levels, you can't beat lots of prop injections. It all depends on your supplier I guess, but I haven't seen that enanthate is that much cheaper than omna.
I personally think that omna/sust are preferred over enanthate because they kick in faster....this is a bad thing, but when people notice results in a couple of days from the fast esters, they start to extrapolate and think they are gonna be ronnie coleman in 8 weeks.
To sum up my opinion: Stew is right, injecting a blend of long and short esters will cause more test fluctuation than enanthate on the same injection schedule and WAY more than prop injected more often....but...use what you can get. It doesn't make that much difference. If you use omna/sust, do 250mg every 3 1/2 days rather than 500mg every 7 days.