I would like to use two 5-pair 110-connecting blocks with both data and POTS. Four pairs of each connector block being used for two data jacks and the two slate pairs to provide two separate POTS lines [phone & fax] in the same location using three 4-pair CAT5e cables, leaving two pair unused. Does this sound as if it would be acceptable or would data interference and crosstalk be a problem.

It's not the best way to do it, but there's no reason why you can't. 110 hardware is rated for CAT5 performance at a minimum and at all terminals.

Personally, I'd terminate all cables on separate four-pair clips and just manage my cross-connecting accordingly. That way you aren't committing to an "all or nothing" wiring infrastructure. Flexibility is the key to doing it right.

Thanks for the reply Ed,
I’ve never done it this way before, so thought I would ask and save some potential headaches.
There are only two slots available on the wiring block and a big problem to add on, otherwise I would do things a lot differently.

I may just be old school but I like 66 blocks for phone and 110 for data. It does make it fast to isolate the various runs if they home run to the 66 and get punched on different rows with bridging clips separating each from the bussed "line" side. (Punched with the "no cut" end of the tool).