CNC Conversion

I've been working on my CNC conversion for my Rong Fu Geared-Head mill/
drill with a 4" circular column for a while and have been getting
increasingly frustrated with the circular column. I'm considering selling
the Rong Fu and buying either a small mill with a knee, something like this:

<http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=12584&item=1921280284>

Or, getting a mill/drill with a square column. Something like this:

<http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3100677129&category=12584>

The latter seems to have a lot of nice features (relatively small,
compact, most of the work I've done on the Rong Fu will transfer as the
side plates/screws are the same size..etc.) However, a new square column
mill/drill is a bit more expensive than a used small mill like above (I
haven't found many used square column mill/drills!), and it appears that
the small mill would be a little more rigid as the square column mill/
drill still has a very wimpy attachment point at the base of the column
(One of the problems I have with the Rong Fu is you can get almost 0.002"
flex by pulling down on the head).

Has anyone had any experience converting either of these to CNC?
Currently I'm leaning torwards the square column as, other than the round
column, I'm really happy with my Rong Fu...

Thanks,

--C.S.