All in title.
I am wondering if there is any alt-coin with 8mb block-size limit that we can run tests on ,
to get some ideas about what we are running to if we increase the block-size limit in bitcoin .

This is a silly question because there's no reason for any altcoin to have blocks even 1/10th the size of bitcoin. Take litecoin for example. Many blocks, if not most blocks have zero transactions other than the coinbase. Block sizes are 2-10KB. LTC has <1% the number of transactions /min of BTC. LTC could have 100MB blocks and it would make no difference - there's not enough volume of transactions to come close to filling blocks whether large or small.