I have tried keeping a bentgrass green in a climate similar to yours the past few years. In my area, the golf courses are about 1/3 bermuda, 2/3 bentgrass putting greens. But, there is a definite trend in golf courses in my area switching to ultradwarf bermuda. Before I started, the golf super at my local course asked me this, "What do you call a bentgrass putting green that looks good 11 months of the year?" His answer was, "A dead putting green." Before I started, he wagered that I couldn't get it through even one Summer. And, this has been my experience. I lose some degree of the bentgrass green ever year, I can even get it looking good through the end of July, but I always lose a good portion of it some time in August. So, I have given up completely, and I bought some Tahoma 31 plugs and am in the process of making a little chipping green. If you want to do a bentgrass putting green that you will kill once the Tahoma 31 emerges from dormancy, I can see that working well for you. But for me, with my budget and my schedule, I didn't have the resources and time to maintain bentgrass successfully. Maintaining a bentgrass putting green in the Fall, Winter, and Spring, is a whole lot of fun. Most of my yard is Zoysia and I love being outside and having something to maintain when the zoysia is dormant. What you have done so far is truly first class with your Tahoma 31, really excellent work. Golf Course maintenance crews are truly artists and scientists, and I have a new and lasting respect for how difficult their job is, and what they are able to achieve in spite of golfers often times abusing the golf course.