All the answers above have missed one key point - what projetors are you using??

There is no one signal that is beter or more appropriate than another - it really depends upon the output device and what control you need over the signal to it

DVI / RGBHV / SDI / HD-SDI all have drawbacks. If you need to subtly change the colour levels between 2 mismatched projectors, you cant do this with anyting apart from RGBHV. DVI/SDI do not have the same amount of control in most projectors.

Distribution of SDI or HD-SDI is simplist - ie singe BNC. SDI can go in excess of 100m decent digial coax, available from most AV resellers. HD-SDI will do 50m on the same cable - Ive not tested further... Also less prone to interference due to nature of signal.

Fiber is not prone to interfeence, but is more expensive and will increase fame delay at every re-conversion. Benefit is that you can transmit most signals over fiber by changing the io box.... but it can be expensive and fiber conectors are not as reliable as they could be. Its the only way to go to transmit DVI over a distance (despite TV-One DVI over Cat5 - there are some drawbacks...)

Cat5 can be a pain and Ive had bad experiences of interference with a number of different cat5/6 transmission systems...

Good old 5wire BC - best way of distributing RGBHV - just be careful with routing to avoid interference. Usually reliable - and you can actually send any of the above signals down the same cable - except DVI (not at the same time though!!!)

So for instalation Id use decent multicore 5 (or more) wire BNC, to give best signal flexibility. If you have the budget, install fiber too as it allows for future compatibility of a range of equipment. If yo do both, then you may as well install a few cat5's too, as the cost will be negligable - this could be used for control too or conversion if desperate

For HD-SDI conversion with low latency, look at the TV-One range (CS2355) less expensive then image-pro HD (and actually available in less than 6 weeks!!!)

To pick up on your questions - when compared to RGBHV at 1024x768, SD-SDI is lower resolution - conversion to HD-SDI is 720 (less) or 1080 more (but upscaling from 1024x768 example) So if connected to TH2G makes little sense, apart from ease of distributing SDI. ***Any signal conversion will cause signal delay*** If live images are to be shown - you need to think about this.

Go look at cost of kit vs your budget. A single fiber converter (one end) will cost you £300 upwards. an RGBHV DA will cost you £60-£150. A fiber matrix will be thousands......

Video is not like lighting or sound - in terms of parching / routing / signals. DMX over ethernet is easy - Soundweb is easy. Video signals are not and cannot be treated in the same way.... avoid patch bays and peripheral processing kit - Keep it simple!

S