InnoDB: Right For Write-heavy Table? Server Tuning?

I've decided to merge 4500 identical tables into one. They were previously partitioned with one table per user of the system, but I'm imagining I may not need to do this anymore for this particular table. I'd like to do so to reduce the number of files in this database's directory (currently over 15,000), to reduce backup complexity, and maybe improve performance. That's where I'm still unsure.

This is the summary table for W3Counter with fields website_id, date, unique_visits, return_visits, page_views. The website_id and date uniquely identify each row.

It is a write-heavy table (probably more than 99% INSERT/UPDATE compared to SELECT). I may be making things up, but I believe I remember InnoDB showing superior performance for this type of table. I'd imagine row-level locking would decrease lock contention when being hit by dozens of threads concurrently -- queries trying to update different rows would be allowed since that row isn't locked, unlike MyISAM where the entire table is locked by each query.

Merging all the tables into this one would mean starting with about 1.5 million rows and growing about 4500 per day.

So what do you think? Is InnoDB the right way to go for this table? Should I expect better performance than MyISAM for the inserts/updates? Should I expect the same or better performance on SELECTs that SUM() those counts over various date ranges, and sometimes group by WEEK(), MONTH() or YEAR() on the date column? I'm not sure whether the primary key is sufficient for that type of query, if a key on just the website_id would help those, or what. Any opinions?

My other reason for this thread is to get some pointers on tuning the server variables for InnoDB tables. There's much less written about this than those mainly applicable to MyISAM tables. Which are most important for a table like this? Right now no other tables will be InnoDB as the rest benefit greatly from MyISAM-specific features (like prefix compression on indexes and maintenance of row counts).

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