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Right, I haven't decided yet. BTW, what would you estimate is the effort write a minimal SPV client library from scratch?
Define minimal. bitcoinj is the result of years of work but that wasn't full time effort, and some of that time was spent on things like documentation, example apps, lots of unit tests, performance optimisations, implementing Bloom filtering on the C++ side etc. You could ask Maxime who did the C client as he did it more recently, though his code is less complete than bitcoinj.
That would be me -- he, I'm not quite done and I prefer not to quantify the time I spent on this

I tried to not cut too many corners for the most part and I wasted time (i.e. had fun) re-implementing a poll loop, an async network i/o stack and various generic libraries. But assuming you re-use existing building blocks, have copious spare time and are proficient in C#, you could get there in a few weeks.
You'll soon be able to look at/re-use bitc code. In any case, feel free to ping me if you have any question. Cheers.