Firstly Brian it's great to see Ireland still at the forefront of European aerobatic flying. Hopefully your home brewed bipe will add to a long list including composite construction, 4 strokes, electric power, contradrives to name a few.
Like Doug I would be wary of sweepback. It moves the aerodynamic centre of the wing back and with it the neutral point of the aeroplane and so you are negating the increase in yaw stability you will be gaining by moving the wings forward. Yaw/roll couple is always a problem with bipes which is why you see the latest designs moving the wings closer together and introducing anhedral to the top wing. Anything that promotes yaw/roll couple, even if it is with angle of attack is to be avoided.
Moving away from the aerodynamics for a minute, remember I commented to you at the Triple Crown that your Mid Rex only looks like a bipe some of the time flying through the schedule? To me its important that it looks like a bipe the whole time and its something your Venture did very well. You might think about this when you position the wings with respect to one another and the fuz. The yaw/roll couple with wing separation needs to be addressed and one area where small improvements might be made is in the vertical centre of gravity of the model. I suspect that getting the weight i.e. the batteries as low as possible may help a little.
Structurally the flying surfaces need to be as stiff as possible. To this end I'm not keen on film covering and I'm certainly put off the Biside by the instructions on how to remove the warps due to the very light balsa used in the construction to make weight. I think you need to consider imaginative solutions such as fully geodetic construction which with laser cutting is not difficult. An all flying tail is a great idea, has been proved aerodynamically on the Biside and does away with control surfaces to warp so perfect for geodetics. Actually the same argument applies to the wings. Ailerons are just something to warp so why not do away with them and go for all flying wings also geodetically built? This isn't as daft as it sounds with the wing panels pivoting on thin section ball raced tubes and driven by S-bus high voltage servos. There is one now which gives 38kg.cm of torque and 0.082s/60deg! As an aside HV S-bus is looking to be a great way to go weight wise, with two servos in the tail and four in the wings and one 3 core cable feeding them. I know that camber is more effective than angle of attack at changing lift but years ago there were a few successful aerobatic soarers which used wing twist and they flew very well.
I hope this might give you a few ideas to play with and you know the address to send the plans to!
Malcolm