Just checking, are you using PDO_ODBC or PDO_INFORMIX? 

Also, how are you fetching the data, are you doing bindcolumn or just a standard fetch into an object/array?

I haven't benchmarked against PgSQL, but when I did earlier benchmarks fetching vs direct fetches using dbaccess it was very close in performance. 
As you said, the connection overhead is real if you are doing a connect on each request, but it sounds like you have a solution for that.

Just checking, are you using PDO_ODBC or PDO_INFORMIX? 

Also, how are you fetching the data, are you doing bindcolumn or just a standard fetch into an object/array?

I haven't benchmarked against PgSQL, but when I did earlier benchmarks fetching vs direct fetches using dbaccess it was very close in performance. 
As you said, the connection overhead is real if you are doing a connect on each request, but it sounds like you have a solution for that.

I am not sure if this is helpful but I just put together a speed test here which had pretty consistent results. It was fetching 25mil rows from a table of fake contacts into a php array.

This was fetching it into FETCH_NUM vs FETCH_OBJ vs FETCH_BOUND

All were select first 25000000 * from names;
Except for array by name which was spelling out the field names rather than just using *.

The times do count the connect and disconnect from the database. I included the memory used just out of curiosity. 

Results:
Array: 35s - Memory: 18877336832
OBJ: 41s - Memory: 28145764120
Array by name: 29s - Memory: 19145764120
By Bound Column: 26s - Memory: 268834832

Interestingly doing "unload to /dev/null select * from names" in dbaccess took 45 seconds. I did not do an equivalent esqlc program to do a full apples to apples. 

I am not sure if this is helpful but I just put together a speed test here which had pretty consistent results. It was fetching 25mil rows from a table of fake contacts into a php array.

This was fetching it into FETCH_NUM vs FETCH_OBJ vs FETCH_BOUND

All were select first 25000000 * from names;
Except for array by name which was spelling out the field names rather than just using *.

The times do count the connect and disconnect from the database. I included the memory used just out of curiosity. 

Results:
Array: 35s - Memory: 18877336832
OBJ: 41s - Memory: 28145764120
Array by name: 29s - Memory: 19145764120
By Bound Column: 26s - Memory: 268834832

Interestingly doing "unload to /dev/null select * from names" in dbaccess took 45 seconds. I did not do an equivalent esqlc program to do a full apples to apples. 

Just checking, are you using PDO_ODBC or PDO_INFORMIX? 

Also, how are you fetching the data, are you doing bindcolumn or just a standard fetch into an object/array?

I haven't benchmarked against PgSQL, but when I did earlier benchmarks fetching vs direct fetches using dbaccess it was very close in performance. 
As you said, the connection overhead is real if you are doing a connect on each request, but it sounds like you have a solution for that.

I am not sure if this is helpful but I just put together a speed test here which had pretty consistent results. It was fetching 25mil rows from a table of fake contacts into a php array.

This was fetching it into FETCH_NUM vs FETCH_OBJ vs FETCH_BOUND

All were select first 25000000 * from names;
Except for array by name which was spelling out the field names rather than just using *.

The times do count the connect and disconnect from the database. I included the memory used just out of curiosity. 

Results:
Array: 35s - Memory: 18877336832
OBJ: 41s - Memory: 28145764120
Array by name: 29s - Memory: 19145764120
By Bound Column: 26s - Memory: 268834832

Interestingly doing "unload to /dev/null select * from names" in dbaccess took 45 seconds. I did not do an equivalent esqlc program to do a full apples to apples. 

Just checking, are you using PDO_ODBC or PDO_INFORMIX? 

Also, how are you fetching the data, are you doing bindcolumn or just a standard fetch into an object/array?

I haven't benchmarked against PgSQL, but when I did earlier benchmarks fetching vs direct fetches using dbaccess it was very close in performance. 
As you said, the connection overhead is real if you are doing a connect on each request, but it sounds like you have a solution for that.