I routinely run DT40 pros at 40k at 8 degrees or 35k at 12 degrees with fairly good results. Content quality, tuning and mirror size are part of the equation, of course.
Pt40s (these are not the wide versions which are pt40a) from Omar at eightonlight are a great value and I routinely push them to 40k at 8 degrees and they do quite well. Not perfect ILDA test frame precise, but more than adequate for viewing most content. I'd call these the best bang for the buck for 40k capability although I'd get Saturns if money was no object.
As always, your mileage may vary and the details of your particular needs and the realities of your budget may drive you to other alternatives.
-David
"Help, help, I'm being repressed!"