Hmm hard to say without benchmarking. The load times are some milli seconds lower, but not worlds. The bottle neck with Matukio and most of Joomla is probably also the database queries / SQL, not PHP (the most intensive php task we are doing is generating PDFs, this should receive a little speedup).
That does not mean that it is not a very good idea updating, you have more performance, security etc. and we can use cool new PHP features sooner
Currently we still support PHP 5.3.10, which prevents us using many new features..
Cheers
Yves