Chris,
You have what may be an exception to all the rules: if your circle is limited to 29' lines, and you are using an .061, you may actually need the extra drag of the lines? But you probably have to compensate with some extra tip weight or offsets. If you drop back to an .049 you probably want to try the Spectra. If you go to longer lines you definitely want to try the Spectra, or the steel cables which I believe would provide maximum performance. What prop are you running on your setup?
I have a Lil Satan on 26' Spectra (30 lb test) lines that has a Black Widow .049 running a Master Airscrew 6x3. It turns rapid lap times. But it hangs out there pretty good, too. It could use longer lines, but I have not experimented at all yet. (The 26' lines were called out on the plans.)
I fly a Baby Clown with Medallion on .008x42' stranded cable. Engine near peak, it will do all the stunts that I can do--and certainly more. Decent line tension until the wind comes up. The setup will actually do a 4-2 run, but then it doesn't have the authority to do all the maneuvers, and the problem is compounded in the wind.
I fly a SIG Baby Skyray for a trainer on .008x42' stranded steel. Cox Baby Bee with a Cox 6x3 flexible prop. It has a big steel fender washer for tip weight. It makes a great initial flight trainer since the lap times are pretty slow, and will fly in a good breeze without coming in. I find that you are not going to get a brand new trainee to back up to maintain line tension. This combination solves that problem.
Some of the local guys fly .061 stunt planes on about 42'. They scream them out for airspeed and line tension and it lets them do full patterns--at a pretty high speed. Faster than my reflexes, anyway.
So somewhere in the middle of all these there should be a good combination for you.
Best of luck,
Divot McSlow
PS--What I am waiting for are the results of Larry Renger's Foam-fold wing stunt plane setup. The reason is that he has an external tank on a product engine in a stunter. Getting the engine to draw consistently thru the full tank and hold a good setting..... Anyway, I have a Guillows P-40 kitbash that awaits engine and tank installation. So far I have a stock Killer Bee backplate and a custom metal tank running small plastic tubing. I worry about the tubing being too restrictive. I think Larry drilled his venturi for more power. I know he had some fueling issues related to plumbing. This type of setup opens up the possibility of a decent reed valve stunt plane that will do the whole pattern using cheap and available parts. What's not to like?