I haven't heard of the outfit in your link, so can't comment.

It is true that Siberian roe deer are bigger than european roe deer but they are not considered the same variety (subspecies?) - a very good european trophy would be in the 480g range (dry net, maybe 570g+ full skull) whereas I understand a siberian can be 1000g+.

It depends where you want to hunt. I honestly believe that some of, if not the best european heads consistently come from the south and south west of England. If you want to hunt in the UK, I can probably put you in touch with a few people.

If you want to hunt roe in Europe, Poland would be a good bet, as would Austria, Switzerland and a few others. Spain has some great hunting, but roe are less abundant there and generally more expensive.
I have used these guys before for hunting in Europe - they may or may not be better or better value than others, but at least their website can really whet your appetite!! http://www.limpopo-travel.dk/frontpage/index.aspx?lang=25&tourtype=2&sitemode=1

Feel free to get in touch if you want to discuss....
Either calibre you mention would be ideal.