I don't know what the others are going to say, but I would go with a dedicated guide scope and any of the guide cameras you mentioned should be ok. With an OAG, your are going to perhaps face framing issues to get a suitable star on the guider prism, and with a guide scope set up, you will need to overcome differential flexure problems. Also, I believe focus travel on the 254 will be an issue, preventing an OAG being used. OAG user please jump in here.
Nothing is cut and dried here, there will alwys be those that are for and against. You need to decide which way you want to go and whether it is in your budget.
Check out this guide scope package for reference.
https://www.bintelshop.com.au/Images/Stock/8162X.jpg
Cheers!
