As though you did not try, you will have a loss, for the simple reason, you do all on the interpreter, and the muscle works on With and as a result we have already ready compiled code. With other things being equal you do not receive more productivity, loading on the processor will grow only, spherical hostings put rigid frames, the muscle since you get rid of it will not hang up, there will be no resources on PHP with yours basis, and again there will be "hang" or locks.
As a matter of fact you should make the same muscle only on PHP. A question - what for?
Probably you can benefit somehow if replace standard SQL with any special requests, probably even not clear to the person or at all a text type.
Into the account of hangup of a muscle - the first time such I hear, as a rule it "hangs up" because of curve requests and shortage of storage including virtual.
If you do not accept neighbors in the server, buy VPS/VDS - now the prices very much even comprehensible, were practically made even to a spherical hosting, but you receive the full freedom, including a muscle and its analog , with the big resources.
I work in this sphere years 10, there were problems because of an overload of a spherical hosting, change of the operator or more expensive rate solved a problem completely.
Anyway on a rate 60rub/month you do not launch shop with thousand goods and thousand visits a day, and on heavy systems, especially.