It looks like you are using InnoDB as your primary database engine type, but you configuration has no InnoDB configuration tuning options, which means you are using the defaults. These defaults, out of the box are sized for an 8Mb machine!
I recommend these settings as a basis and work from there
innodb_file_per_table
set-variable = innodb_buffer_pool_size=2G
set-variable = innodb_log_files_in_group=4
set-variable = innodb_log_file_size=128M
set-variable = thread_cache_size=10
set-variable = table_cache=512
set-variable = query_cache_size=8M
You didn't say if the php site was sharing the same machine as your db server, so you will have to be careful that MySQL doesn't consume so much physical ram that it causes the machine to swap.
I'd also recommend that you add these settings to low slow queries and queries with a poor query plan.
log_slow_queries
log-queries-not-using-indexes
set-variable = long_query_time=1
Both platforms use the same mechanism for replication: Galera. On the page at that link, you'll notice there are images featuring both PXC and MariaDB Cluster.
Galera library provides transactional replication. MyISAM doesn't do transactions, so the problems you may be having now are very likely related and would not be any different on the alternate platform.
Currently replication works only with InnoDB storage engine. Any writes to tables of other types, including system (mysql.*) tables, are not replicated. However, DDL statements are replicated in statement level, and changes to mysql.* tables will get replicated that way. So, you can safely issue: CREATE USER..., but issuing: INSERT INTO mysql.user..., will not be replicated.
— http://www.percona.com/doc/percona-xtradb-cluster/limitation.html
Currently MariaDB Galera Cluster only supports the InnoDB/XtraDB storage engine.
— https://mariadb.com/kb/en/getting-started-with-mariadb-galera-cluster/
And, of course, PXC uses XtraDB, Percona's compatible replacement for InnoDB (it has "XtraDB" right in the name), and MariaDB also uses Percona's XtraDB instead of Oracle's InnoDB, although, for compatibility on both systems, the storage engine still calls itself InnoDB.
Since the two systems share a signficant amount of code and are all intended to be essentially drop-in replacements for one another, the decision of which platform to use is largely a matter of opinion. I personally prefer vendor "x" which might mean I'd personally recommend you use MariaDB and also might mean I'd personally recommend sticking with PXC, but I need not actually actually tell you my preference, since it doesn't matter -- it's based largely on opinions and impressions and documentation and personalities and not on any kind of valuable evidence.
Your best solution for migrating MyISAM is probably going to be to modify the dumpfiles to ENGINE=InnoDB (and any other changes that necessitates) or staging them on a standalone server, then converting and exporting them as fully-InnoDB before trying to import them to your cluster.
If the MyISAM issue is your only concern, or even just your primary concern, then MariaDB Cluster and PXC are essentially identical in that regard -- they don't support it, for a very sensible reason -- it's not feasible to do so.
Best Answer
This is the use case for MySQL Cluster.
Check out Percona XtraDB Cluster (based on Galera) for a similar (i.e. synchronous) solution for use with web applications. Note that it is an alpha release but it is probably the most promising solution out there today. Schooner also has a synchronous solution. There is also Continuent's Tungsten although it is an asynchronous solution.
Hope this helps.
Cheers