House Edge is unaffected by penetration...
Vytas,
"House Edge" is calculated for straight Basic Strategy for a deck (or shoe) that is freshly shuffled for each round. To get the HE for this game, I used Don Schlesinger's incomparable BJA3, Table C1, Pages 492-3.
1. Benchmark (S17, DOA, NDAS, SPA1, SPL3, NS) for SD: +0.033
2. SPA3: +0.032
3. DAS/SPL3: +0.141
4. BJ 6:5: -1.395
Summing these gives a HE of -1.189%... Good Luck!
Now if you want to know the IBA for a card counter... that's a different story and depends on several factors:
1. What CC system are you using? Clearly, a high P.E. system will be able to take better advantage of the 100% pen.
2. What spread are you using? Since the fraction of +EV rounds will be much smaller than for a 3:2 game, when they do occur you have to take full advantage.
3. What playing conditions can you expect? Heads-up play would be best, since you'll have no unseen cards when you make your playing decision.
The only time I have willingly played 6:5 (I have once or twice been mislead by deceptively inadequate signage) was on a game such as you describe in pre-Katrina Biloxi back in my red-chipper days. I was able to gain an advantage during heads-up play with a $5-$100 spread. I doubt a 1:20 spread will be tolerated long for green (or higher) play ;-)
Hope this helps!
Dog Hand