I've lost sight of where TTL is currently at...
However, the recent postings seem to be leading towards a naval 'arms-race', principally between Portugal and Istanbul. Going back over the Lepanto issue gives two fairly good arguments for and against an Ottoman victory; which to my alt-his mind indicates a fair possibility of either occurring and so there's little evidence to conclusively make Lepanto a make-or-break factor in the development of TTL.
Any discussion of technical advance/limitation must IMHO take into account spurs to technological development. I think that the onus is on the Ottomans to demonstrate that they can take the initiative in naval/maritime technology given the reasonable observation of the OTL Ottomans technical conservatism. The OTL dominance of Portugal in naval/maritime technology was to a large degree what took her into the Red Sea and Indian Ocean and I think there is a reasonable case to argue that for the purposes of TTL the Ottomans may well be able to prevent an eastwards expansion by western European powers. Though again I'd have to place the emphasis on the pro-Ottoman posters to give an alt-his of Ottoman advances in this area.
Given the proposition that the Ottomans shut off an eastward sea route, or at the least, in the absence of a definitive Lepanto, make an eastward passage commercially risky, we have the issue of a greater emphasis on westward exploration/exploitation and potentially an anticipation of the work of Henry the Navigator. There are substantial Atlantic challenges that need to be overcome, but they were overcome OTL so there is little to suggest they couldn't pre-empt these developments TTL.
I feel the issue of Italy will to some degree be a paper tiger given a substantive blunting/nullification of Western naval power in the Mediteranean and that, indeed, "Better a turban than a Cardinal's cap". Though I'd possibly widen that pragmatic sentiment to move from a religious to a wider political sense. Given the history of Italy as a plaything of the greater European powers, there is a case to be made for the welcome mat being put out for an eastern power that tends to promote stability (and to be fair the other side of that coin, stasis). In one sense, there's a case to be made for Italy to be conquered 'de facto' given it's main connection with Europe may now well become the Alps. With a lack of blood and gore, regime change becomes easier to accept.
Given the parameters of non-unified Spain and France, this gives a stronger westward orientation to western Europe, a tightening of Ottoman influence over 'Arabic' east Africa and India, and a likely military deadlock centered somewhere around Austria. The roles that Africa and the Russias play hasn't been touched on particularly, and I still have doubts about the Ottomans ability to make their ascendancy permanent (that 'why' question again). I feel that working through the Iberian/Sicilian apostate issue may throw light on how the Ottomans might obtain a permanency.
Croesus