Hi Bojan, I got your PM and thought it might be best to respond on your public discussion thread.
The length of the speargun you choose should mainly be a function of the visibility/range that you will normally encounter, which is largely a function of water clarity. In the Med. folk seem to use mainly 75-110cm guns from what I can tell; here in the UK 70cm-90cm is more common, we tend not to use reels (our fish are usually much less than 10lb/4kg) but med. spearo often use reels I believe. Find out what the local spearos where you plan to fish use (re. length & reel). Folk tend to get hung up on power and range, when often a smaller, less powerful but more nimble speargun will work better in poor visibility (the Italian World Champion that used the Cressi Comanche reputedly used the 60cm and 75cm models).
I am only (somewhat) familiar with the Cressi Comanche - which was used by an Italian World Champion a few years back - it's a very good gun that is usually/often reasonably priced. Parts seem to be more readily available for it than anything else I have come across.
Re. the Salvimar Voodoo rail open 85cm, I have never heard of it before but it looks interesting/good. I see a bulk rubber ("Voodoo Rail Open") and a screw-in rubber muzzle ("Voodoo Rail") versions on the web:
I prefer the look of the bulk-rubber version but screw-in rubbers are probably more common in europe. Rails are nice but make little difference on shorter guns - but with a non-directional bulk-rubber muzzle, probably a good idea. Looks like the second one offers the ability to use it open or closed muzzle (my Omer XXV has this ability too, I use the close muzzle option currently but plan to try the open muzzle option in the future). Articulated metal wishbone - normal in europe but I prefer the soft dyneema-cord wishbones on South African railguns - but you could change that later, if you cared, I suppose.
RE. Seac Sub Bolt 85cm, I've never seen that before either. Again, looks good:
Screw-in rubbers, side-line release (on the opposite side to my Omer XXV by the look of this image - but it might have been reversed). Muzzle loop could potentially be used with bulk rubber loop (as sole or secondary band). Handle & rear look a bit like the X-fire - nice, modern.
The Cressi would be the safest bet, because the company and model are well known and well regarded, and well supported. However both of the other spearguns look like good designs. How well the trigger mechs. work/last remains to be seen. Find out what kind of warranty/support you will get from (1) your supplier and (2) the manufacturer.
You might also want to check out the Omer Excaliber & Omer Cayman models from Omersub.it (the regular aluminium tube variant is probably all you'll need - there are carbon and hydro-formed HF and HF2 variants that cost more). The Cayman handle and trigger mech. is pretty much state of the art.
I hope that helps. Perhaps other will add their thoughts.