Wordpress blog where pages are almost-always served from cache: SSD or more RAM?
If you are going to put MySQL in a wimpy environment (WIMP = Windows, IIS, MySQL, PHP/Perl/Python), your first priority needs to be RAM. Please get more RAM on the box.I suggest 32GB.

As for MySQL, you need to tune InnoDB as much as possible. Here is the InnoDB Architecture

InnoDB Architecture



Recommendation #1

By default, 25% of the Buffer Pool is used to process changes to secondary indexes. Thus, I suggest double the amount of data (you said 3-4 GB) as the Buffer Pool Size

innodb_buffer_pool_size = 8G


Recommendation #2

Since you have a dual core machine, split the Buffer Pool to prevent swapping

innodb_buffer_pool_instances = 2


Recommendation #3

You will need good read and write I/O threading

innodb_read_io_threads = 16
innodb_write_io_threads = 16


Recommendation #4

You need to the Log Buffer to be larger for increased write performance

innodb_log_buffer_size = 64M


Recommendation #5

You need the Log Buffer flushed often since you are in Windows

innodb_flush_log_at_trx_commit = 1


CAVEAT #1: The default for innodb_flush_log_at_trx_commit is 1 to maintain ACID compliance. Do not change this in Windows since Windows has the final say on disk caching.

CAVEAT #2: There is an option for InnoDB to cache data instead of letting the OS do it called innodb_flush_method. Unfortunately, the setting O_DIRECT is not available for Windows. If you switch to Linux, setting this option takes disk caching by the OS out of the equation.

Recommendation #6

Sequential and Random Reads from SSD can be the same or a mixed bag depending on the model SSD you get. If your IOPs exceed 10,000, you can change innodb_io_capacity to 10,000 and innodb_io_capacity_max to the maximum IOPs.

Summary

Get 32GB of RAM for the WIMP machine and use these setting in my.ini

[mysqld]
innodb_buffer_pool_size = 8G
innodb_buffer_pool_instances = 2
innodb_read_io_threads = 16
innodb_write_io_threads = 16
innodb_log_buffer_size = 64M
innodb_flush_log_at_trx_commit = 1
innodb_io_capacity = 10000
innodb_io_capacity_max = (Maximum IOPs of the SSD)


Alternative to SSD Only

If you are will to configure it, there is a design that a Facebook Engineer uses to split up InnoDB tables and logs to lengthen the life of the SSD by writing the sequential stuff for InnoDB (Double Write Buffer, Log Files) to a fast HDD.

I have discussed this before


Feb 06, 2014 : MySQL on SSD - what are the disadvantages?
Aug 14, 2013 : How do I determine how much data is being written per day through insert, update and delete operations?
Jun 25, 2013 : Postgres Write Performance on Intel S3700 SSD
Jun 18, 2013 : How big can innodb_doublewrite_file grow?