The original Porta mount is a good mount. I'm not sure how much better the Porta II is.
I still use mine with a TV60. I have used it for a Megrez 90 and that was also very suitable. Here is a review I wrote not long after I first got it.
http://www.iceinspace.com.au/44-353-0-0-1-0.html
I think a 4 inch refractor might be pushing it.